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Description

Goliath is an open source prototype vehicle for developing gas-powered quadcopters.

Details

Overview

Goliath is a prototype vehicle for developing large scale quadcopters. The current design is based on a single central gas engine with a belt drive providing power to the four propellers. Control of the vehicle is provided by control vanes placed under the propellers. Each propeller will be enclosed within a duct that protects the rotors and contributes to the lift. Goliath itself will be open source with the creative commons license, and whenever possible open source components are used.

The Mk I vehicle was focused on developing the drive train. The Mk II vehicle was built with lighter weight aluminum frame. Even when completed Goliath is intended as a starting point for future vehicles.

Flight control will be performed using the Pixhawk controller running the PX4 flight stack.

Related Projects

Current Status: HOVERING!

The Mk II vehicle has been assembled and hovered for the first time in September 2016.

Details

Structure

The initial Mk I frame was constructed using slotted galvanized angle, also known as Dexion, bolted together. While this is heavier than a steel tube or composite frame, the dexion is quickly assembled and can easily be reconfigured. This allowed for multiple iterations of the drive system to be tested with a minimum of time and cost.

The Mk II frame is built using aluminum tube and assembled using aluminum gussets and and stainless steel rivets. This leads to a lightweight, vibration resistent design that can be assembled easily.

Engine

An electric powered design would have been the most straightforward approach. Electric motors are more efficient than gas motors, but the energy density of gasoline is much greater than today's batteries. So until battery technology improves, for large scale vehicles, gas power seemed the way to go.

Goliath currently uses a single 30 Hp vertical shaft engine and a belt system to transfer power to the four propellers. The setup was chosen because at this scale, four smaller gas engines have a smaller power to weight ratio than a single larger engine. The specific engine, an 810cc Briggs and Stratton Commercial engine was chosen primarily because of its relative low cost per power ratio.

Drive System

The drive system uses High Torque Drive (HTD) belts. These belts are made of neoprene rubber with continuous fiberglass cords. HTD belts are able to transfer more power per weight than roller chain and can also run at higher RPMs that Goliath requires.

To eliminate aerodynamic torque, the drive system rotates two propellers clockwise (CW) and two counter-clockwise (CCW). This is done by using two belts, one sided sided and the second double sided. The direction of rotation is changed by placing the outside of the double sided belt against the driving pulley.

Propellers

The propellers are fixed pitch propellers 36 inches in diameter. They are custom made, starting from a foam blank with birch stiffeners. The blanks are machined using a CNC router and then fiberglass and epoxy are laid up over the machined core. This process produces a propeller that can carry over 60 lbs while only weighing one and a quarter pounds.

Control

An electric quadcopter would traditionally maneuver by varying the speed of each propeller to control thrust. Since Goliath uses fixed pitch propellers and all the propellers turn at the same speed due to the belt drive, maneuvering will be done by control vanes similar to those used to steer hovercraft.

Exhaust

Each of the two exhaust pipes are built from Go-Kart hardware, which are easy to procure and inexpensive. The U-Build It Kits are easily assembled using a minimum of welding and highly customizable.

Electrical System

The electrical system is powered primarily from the alternator with the battery as a backup. The battery is 12V and designed for off-road vehicles, so it'll handle high vibration loads. The micro-controllers and servos...

Project Logs

Progress is being made the flight controls and the hub for the first prototype was attached to Goliath and spun up to make sure it held together (see #EVPR: Electric Variable Pitch Rotor for more details). There were no issues with the EVPR, there was an issue with the flight controller. When the vehicle was activated, the controller didn't power up properly. The Pixhawk consists on an FMU and an IO board. The IO board power was the only light coming on, nothing else. As a work around for this test, the flight controller was removed and I went back to controller the throttle with just a standard RC receiver directly connected.

While I can do a little bit more testing without the controller, it's not going to be too long before I need a new controller to start testing the interface between it and the EVPR. However, I'm a little hesitant to get another Pixhawk as I'm not sure what went wrong with the old one. It was about 3 years old, but there was only a handful of hours on it. There were a few rough tests, before I nailed down the isolation on the avionics tray and Goliath had two solenoids go bad, most likely due to vibration.

I'm familiar with the PX4 flight stack and at least know conceptually how to proceed with modifying the software to work with the EVPR. However there a few controllers that use the PX4 stack including the newer Pixhawk 2.1. Of course it uses different connectors, so the stack of DF13 connectors I have laying around as well as the GPS would be worthless, but maybe it makes sense to upgrade.

Up till now the work on Goliath has concentrated the drive train and the structure. The controls were put on the back burner until the other design problems were addressed. The other items aren't done, but the project has progressed to the point that having a control system would be helpful.

When Goliath was originally conceived three years ago, the default control scheme was to use vanes underneath the rotors to direct the airflow for control. This was chosen because it was the simplest hardware setup to implement and it's been demonstrated to work for hovercraft. Back in October I started doing some basic calculations to size the control vanes and determine the required servo sizes. Turns out assuming that if it works for a hovercraft, it'll work for Goliath was a bad assumption.

The issue with using vanes is the rotor downwash velocity. Goliath has a similar amount of horsepower as a hovercraft, but instead of 1 fan, there are 4 rotors, so the power per area is reduced by a factor of 4. Additionally the equation for the force generated by a vane is:

So if the downwash is reduced by a factor of 2, the force created by the vane is decreased by a factor of four. The end result is that at full thrust, a single vane would have generated only two pounds of force. Which would be grossly inadequate. More force can be generated using multiple vanes in parallel, but the forces would still be low.

I was discussing this issue with @Benchoff at the OSHW summit, and he suggested using grid fins instead. Doing some back of the envelope calculations show that grid fins should generate enough force. The downside is that the the grid fins have much higher drag, which would reduce the payload or flight time.

Ignoring their complexity, variable pitch rotors would be the ideal control scheme. Variable pitch rotors would be able to generate larger moment torques than either vanes or grid fins. However, the increased complexity and the fact that Goliath is already a complex project, convinced me not to pursue this.

However, it's been three years and I really want to see Goliath fly, so I've decided to start building both grid fins and a variable pitch rotor. If I pick one scheme and it doesn't work, then it'll be that much longer before it can fly. So I'll incrementally develop both and see which one works out better.

Grid Fins

The grid fins I'll document as part of Goliath as they are relatively straight forward. I have sourced some material to create the fins. The fins will be made from aluminum louvers for florescent lighting. It was difficult finding sheets big enough to make a 36" disc from, but I finally found some 4'x4' sheets (shown below).

The next step will be cutting out a test disc and placing it under a rotor to determine the control forces generated.

Variable Pitch Rotors

The variable pitch rotors are a different story. I had decided not to pursue this until I came across some research that made me realize that it may be possible to create an electrically actuated variable pitch rotor with the servos contained inside the rotor hub.

I've created a separate project, #EVPR: Electric Variable Pitch Rotor, and I'll be documenting the progress there. I'll be populating more of the design details there, be sure to follow the project if you're interested and want to get updates. Additionally, I think that the project can be useful for other multi-rotors and even conventional aircraft, so I'm entering #EVPR: Electric Variable Pitch Rotor in the 2017 Hackaday Prize. If you think it's worthwhile, but sure to give it a like.

Goliath hovered for the first time in September of 2016. The hover performance was less than desirable since it required a higher throttle setting than hoped and the vehicle did not rise evenly. It tended to favor the port side or the aft. Even more puzzling, was that it tended to lift off first on the side that had the most weight. Ballast could fix the issue, but understanding why is also important. Testing has continued to evaluate the aerodynamics of the setup. Below is a video compilation of some of those tests.

Test 12 was a simple flow visualization of the rotor downwash. Tufts of yarn were added to the frame to show the flow direction along the radius of the rotor and into the frame. The tufts behaved as expected, with the tufts under the rotor mostly steady. Inside the frame, the tufts indicated the flow reversed and flowed upward due to ground effects. While the tufts wiggled, there did not appear to be anything that suggested any unsteady flow phenomena.

Tests were also conducted outside to see if the shop walls and ceiling were effecting the aerodynamics. Occasionally in the past, loose debris had been ingested into the rotors and the debris recirculated inside the wake as the flow got turned around by the walls and got re-ingested. Testing outside reduced the re-circulation.

Test 16 nearly ended up with the vehicle getting damaged. There were four hold-downs, intended to allow the vehicle to move slightly upward, yet remain captive. They weren't made long enough and the hold-downs failed on the aft end of the vehicle. Fortunately, the throttle was reduced in time and the vehicle settled back on the stand (albeit precariously).

The hold-downs were fixed and the testing continued. During Test 17, the vehicle again lifted up, favoring the port side, but at a reduced throttle setting. However, the test stand didn't allow enough movement for a full hover to be achieved. The test showed that the asymmetries were present, regardless.

In theory, the rotors themselves should have been out of ground effect as they were at least one diameter above the ground. However, for quadcopters, it may be that the ground effect is dependent on the length scale of the four rotors together and not the length scale of a single rotor. If that is true, then perhaps the port rotors are experiencing higher thrust since they are slightly closer to the ground. It's difficult to tell exactly. This may be why the Mallory Hoverbike has the offset rotors catty-corner from each other.

I'd hoped to be well into working on the controls on Goliath by now, but the shorter days and colder weather mean less time in the shop. I'm still nailing down some lingering issues with the drive train. The new pulleys are weeping grease because the bearings are getting too hot. I suspect it's because I'm using all thread axles and nuts to keep the bearings in place. I'm working on building the proper axles and axles mounts to go with the new pulleys.

Meanwhile I wanted to document the progress made on mitigating the vibrations that the avionics experience. This was accomplished by better isolating the engine from the frame and the avionics tray from the frame. The new engine mounts are made primarily of rubber, but are built such that if the rubber fails, the bolts are still captive. Stainless steel bolts are used to attach the mounts.

The avionics tray was switched from aluminum to steel. This was to add mass to help reduce the displacement of the avionics tray. Below is the new tray with some of the avionics populated.

The tray is mounted to the frame using four Expansion Nuts. I forgot to take a picture of them before I installed them, so here is a link. Below is a shot showing the flange on the expansion nut between the tray and the frame.

So how much did all the changes help? Data from the Pixhawk shows a huge reduction in the pitch rates down by a factor of 5 to 10. This means that the Pixhawk should be able to control Goliath once the rest of the hardware is complete.

Hopefully the next log update in the not too distant future will be about fixing the bearing issues.

It's been a little over two months since Goliath hovered for the first time. Here are some of things that have gone on since then.

First was a trip to the Portland Maker Faire, September 11 and 12th at OMSI. It was a lot of fun showing off the vehicle, especially now that it hovers. Thanks to everyone who came out and checked out the project. I had a lot of great conversations that weekend.

After getting back to the shop and making sure everything was in working order, it was time to get back to work. The first order of business was to finalize some of the hardware. While Goliath hovered, the center of gravity didn't seem to be in the most ideal location. In order to remedy this, all of the hardware needs to be finalized with the flight weight components, particularly the remaining steel pulleys.

This was the same process as before, but since these are idlers and tensioners, no holes are needed for bolts. The last of of these components are complete, with each saving around a pound of weight. There is now only one one steel pulley left on the vehicle, the main engine pulley.

There was also a hiccup with the battery and solenoid. The battery died, likely because it was undersized and was being deeply discharged. A new bigger battery was added with 18Ah, 80% more capacity than the previous battery, but with only 4 more lbs. Some thought was given to switching from the lead AGM type to a Lithium based battery, which would save about 10 lbs. However, the AGM has been demonstrated to work with the high vibration environments.

The solenoid failed again, the second on that's failed on Goliath. It's obvious that the stock lawnmower ones aren't built for the vibrations that Goliath creates. It was replaced with another stock solenoid as a temporary fix, but a heavy duty one needs to be sourced for the future.

Lastly, the temporary Avionics Tray was replaced with a permanent one. This time it was made from 16 gauge steel. It weighs a little more than a pound. The idea is that the added mass will help to dampen the vibrations. The tray is isolated from the frame. using rubber expansion nuts.

I'll have more details in a future log post, but the great news is that between the new engine mounts and the avionics tray have reduced the vibrations that the Pixhawk experiences low enough for it to work now.

Over Labor Day weekend the assembly of the Mk. II vehicle was completed. The new vehicle was weighed and the current weight is 170 lbs, 50 lbs lighter than the previous vehicle. The first couple of tests were conducted and Goliath has hovered for the first time!

There is obviously a lot more to be done, but hovering is a big step in the right direction.

Also, if you're in the Portland area this weekend, come see Goliath at the Maker Faire!

Work has continued on the Mk II vehicle and it's nearly complete. The latest work has been attaching the idler pulleys, tensioners and the battery.

The ilder pulleys were mounted to same 1/8" plate used for the engine mounting plate. Aluminum angle was riveted around the edges and the plates were bolted to the frame.

Below, the two idler pulleys for the single sided belt are attached.

The center idler for the double sided belt required a different approach. The upper attachment was already part of the engine mounting plate. The lower attachment was made from a smaller piece of plate and riveted to two cross members that were added to the frame. Below is a shot looking at the underside of the frame where the cross members were added.

The other idler for the double sided belt was attached using two different methods. On the lower side, the aluminum plate with angle was used and bolted to the frame. For the upper side just a plate was used was bolted to the engine mounting plate, using the same bolts for the engine mount.

With the idler pulleys all attached and the tensioner attachment method decided upon, some additional gussets were added to reinforce the aft end of the vehicle.

With the aft gussets attached, the exhaust pipes could mounted.

Not shown are the flexible mounts scavenged from the original frame.

Next a tray for the battery was created from angle pieces.

A rubber liner was added to the bottom of the tray.

To keep the battery in place an additional piece of angle was bolted in place on top of the battery.Now all that remains to complete the Mk. II vehicle is to add to the electronics and the fuel tank. With some luck, the vehicle could be complete and running by Labor Day.

Goliath Mk. II will be at the Portland Mini Maker Faire on Saturday and Sunday, September 10th and 11th at OMSI. This will be the first time the Mk. II vehicle will be shown in public. I'm working on completing the vehicle and having its first test before the Maker Faire. The vehicle will not be run at the Faire. Look for it at the McCloud Aero Corp booth.

This last weekend was productive and the major portions of the frame are now complete.

After attaching the engine mounting plate to the frame, the next step was assembling the lower frame. The lower frame is similar to the lower ring of the upper frame, so it was possible to reuse the jig for the upper frame with some minor modifications. This was simply making new wood rotor shaft mounts for the lower frame and swapping them out in place of the old ones. Then all of the lower frame elements were cut and placed in the jig.

With all of the elements in place, the same process for riveting the gussets was followed.

Next the lower rotor shaft mounts were machined out of metal. There was a couple of hiccups due to the double sided tape not holding and bit breaking.

Once the mounts were completed, the shaft mounts were attached with bolts to the lower frame in the same manner of the upper frame.In the future the gussets would be attached to the top side of the lower frame. However, at this stage the method of attaching the idler pulleys and tensioners hadn't been finalized. Therefore the upper gussets were left off at this point.

With the two halves completed, it was time to start attaching them together. Both halves of the frame were attached to the rotor axles to hold the two halves relative to each other. It was easiest to work with the frame flipped over since most of the riveting was on the bottom.

Four lengths of tubing were initially cut and attached on the sides of the frame along with the gussets for the lower frame. Clecos were used to hold the parts together prior to riveting.

Next the lower cross members were added to the lower frame

With all of the new elements attached, it was time to riveting the parts and finalized the attachment between the frames. At that point the frame was flipped back over to see the progress.

At this point about 80% of the frame is complete. the frame members at the front of back need to be added and some smaller cross members need to be added to stiffen the frame. However, before completing the frame elements, the attachment hardware needs to be completed to make sure there aren't any issues with the remaining structure. Once the attachment hardware has been finalized, then the frame can be finalized.

Progress on the Mk. II vehicle is moving along and the engine mounting plate is now attached to the upper frame.

The first step was to start measuring and cutting the tubing that attach the engine mounting plate to the upper frame. This was starting by making a simple jig to hold the pieces at the right elevation to each other.

This worked for doing some preliminary alignment, but to make sure everything fit well, it was decided to redo the jig so that the engine could be placed on the vehicle while it was in the jig. This was done by further elevate all the pieces, with 2x4 blocks holding up the engine mounting plate.

When all of the tubing was cut, the holes were drilled on the ends attached to the mounting plate and the parts were held together with Clecos.

The plate with the tubes attached was put back in the jig and aligned with the upper frame. Then the gussets for the remaining joints were made and attached with more Clecos.

The gussets are wrapped around the tubing and will also serve as the attachment points between the upper and lower halves of the frame. This required bending the gussets with a larger 3/4" radius. To get a good radius bend, the press brake was used with a 3/4" diameter steel bar placed along side the sheet metal to provide the right shape for bending.

Once all the gussets were in place, the engine was mounted to double check that there was adequate clearance, before permanently attaching the plate to the frame.

All of the clearances checked out and with no glaring design issues present, the rest of the rivets were pulled on the frame side of the tubes. Since there wasn't enough clearance to pull the rivets under the engine mounting plate, the frame was flipped over and the last of the rivets in the plate were installed.

A quick note on the rivets for the engine plate. Rivets are designed to join a specific thickness of material. The 1/8" thick plate is thicker than the gussets, so slightly longer rivets had to be used. So care has to be taken to make sure the right rivets are used in the different locations.

At this point, the frame is about 50% complete. The frame was weighed in it's current configuration (without the engine) and weighs 14 lbs, 2 oz. This means that the final structure weight is sill on track to weigh around 30 lbs.

Next up for the Mk. II vehicle is to build the lower half of the frame and machine the lower rotor shaft mounts. Once that work is complete, the two halves of the frames can be joined together.

While Goliath is a big and powerful, it's only as dangerous as the user. As you build, test and fly your giant quad copter be mindful of your safety and the safety of others.

2

Step 2

BUILDING THE COMPOSITES

Building the composite pieces requires the longest amount of lead time. It's recommended to start these pieces first, and the rest of the components likely be built while waiting for the composite pieces. Components made from composites are:

Propellers

Ducts

Control Surfaces

3

Step 3

BUILDING THE UPPER FRAME

A) Build the Jig for the Upper Frame

To properly build the frame, jigs are required to hold all of the frame elements in place. The jig is constructed from particle board. Below the completed jig is shown with the upper frame elements in place.

B) Cut the Upper Frame Elements

Using a miter saw, cut all of the frame elements and place them in the jig to ensure a proper fit.

C) Cut the Common Gussets

Cut the common gussets (4 A & 4 B), layout and drill the holes with the #30 drill bit.

D) Assemble the Upper Deck Elements

1) Remove the frame elements for the upper ring, leaving just the pieces for the upper deck

2) Clamp the common gussets in place and drill half of the holes into the frame. Use Clecos to fill in the holes as you go.

3) With half of the holes filled with Clecos, drill the remaining holes and fill them with rivets.

4) Remove the Clecos and fill in the remaining holes with rivets.5) Remove the upper deck from the jig, flip it over and place it back in the Jig

This is a cool project. When you were building this did you use a Design program when drawing this thing out? Or was this all built from experience? The reason I am asking is because its for college course I am taking. I'm wanting to build this for my CAD project and know if had any previous info like dimensions for the frame? Well, thanks for reading and I will be being staying tune in for project updates.

Have you considered using a variable speed pulley system and an actual quadcopter stabilizing software and hardware setup to control the amount of speed each pulley produces? Servos and actuators incorporated along with tensioners to increase and decrease the amount of speed that each pulley system produces. There are many manufactures of these belts and pulley sets. I personally think that would be the best solution to be able to maneuver this craft safely. If this helps your quest to make a gasoline powered quad please inform me about it. You would need 4 sets of these to manage the quadcopters prop speeds. https://trade.indiamart.com/search.mp?search=variable+speed+pulleys Or you could even use a small electric motor design that manages the amount of tension either with screw type management or offset tensioner pulley on the electric motor that changes each belt according to its thrust using the quadcopters hardware. But the reaction time would suffer greatly by using a screw type actuator just saying that for reference.

If money was no issue, I'd probably try to make my own engine along the lines of #Open Source Two-Stroke Diesel Engine. There are engines out there with higher power to weight ratios, but the peak power RPM isn't optimal, so additional gearing is needed.

For props carbon fiber would give you the lightest weight and if money is not an issue, you could just get 4 variable pitch tail rotors from a helicopter.

As far as a control system, you could just treat this as a singlecopter. The fact that it has 4 rotors instead of one is not really material, since all give the same thrust. The implication is that (a) you only need 4 vane controls, and (b) it's already available in Ardupilot.

I hadn't thought of it in terms like that, but you're right. It looks like there is one difference between Goliath and the Ardupilot singlecopter setup. Goliath is setup as an X configuration vs the Ardupilot singlecopter + configuration. Regardless, it should be something that can be adapted. Thanks for the excellent insight!

I guess its easier to just test with new pulleys at this stage, but I was just wondering if you have considered using a 2 or 4 stroke motorcross bike engine? Light weight, high power, somewhat pricey, but not impossible to purchase. The engine units are generally well separated so the transmission part of the engine can be milled off the engine. Either way its a lot of work to do an engine swap. I can see a lot of work has gone into this project!

Eventually a different engine would be ideal. I had not looked at motocross engines, I'll have to add that to the list. One reason I've stayed with the current engine is that it's inexpensive and if the vehicle crashes I'd rather lose this engine.

which uses only one motor and then uses constant speed propeller blades that use the same system that helicopters use to alter the pitch to adjust the lift of each corner?

I have been thinking of building a similar design of one power system but using one of the Honda silent generators for power then either still using separate motors at each blade or a single motor and belt drive like the Hobbyking Assault Reaper quad.

Hi who did the editing of this page? I am dyslexic and noticed one obvious mistake as soon as I read it ie:- "Oregon and New Jersey have deemed too dangerous for the average citizen to handle putting their own car."

where is the average citizen trying to put their car that is so dangerous ? or did you mean :- "Oregon and New Jersey have deemed too dangerous for the average citizen to handle putting in their own car."

Increase the diameter of the pulley on the motor and add a centrifugalclutch to allow the engine to start and addle be for engage the propellers thiswill allow higher rpm to the propellers. Do this till the motor can’t increaseto the max rpm than back off a little this will tell you if the motor is toosmall. I don’t think it is you just need to get the rpm’s up on the propellers.

And put a cage around it when you test it. I don’t thinkyour propellers will withstand the rpms needed for lift off. If one breaks verybad news for ever who is around.

Any recommendations on specific clutches? I looked around for one that would work my Goliath about a year ago and I didn't find any.

Thanks for the concern about safety. When Goliath is being tested, there is a safety net that is put up, and everyone is behind a big steel tool cabinet. There are some pictures of the safety net in the project logs.

From my experience in the structural world, might I suggest adding a washer under the bolt head to distribute force evenly? Right now, it looks like most of your bolt heads are only gripping a very small amount of the galvanized steel. You are best off using a flanged nut with a washer under the bolt head. I know you're trying to cut weight and washers won't help that but neither will a bolt head pulling through steel :)

Have you looked into lightening the engine itself? some features like the fuel shutoff solenoid are potentially un-needed as those were added to prevent a bad needle valve from flooding the engine during storage. The various covers are potentially replaceable with lighter weight parts. I was briefly interested in using a weed eater engine to power a RC plane, there is a community dedicated to modifying small engines for RC use. I believe some of them modified or replaced the flywheel to make it lighter.

All good thoughts. I haven't concentrated on that area yet. I would like to leave the solenoid in to be able to shut off the fuel source in case there is an engine fire. It's a common practice for aircraft, though it's probably pretty unlikely that I'll have an engine fire and still be able to command the fuel to shut off. The fuel solenoid is pretty small, so it'd not too big of a weight penalty.

The plastic covers would be fairly easier to replace. I could make molds off the existing ones and replace them with fiberglass.

I'd love to get a lightweight flywheel for the engine, that's probably be the most beneficial and it's relatively easy to swap out. I haven't found any out there for my particular engine model.

If you could share any links to the specific RC groups you mentioned that'd be great.

Below is one site that has a bunch of info, they focus on the smaller engines but a lot of it should apply. Also a site that has parts that may be compatible or at least copy-able design wise for your engine.

Very interesting! Great job thus far :).Have you thought of using 2 stroke motors at all? You can generally get more power out of a lighter 2 stroker vs a 4 of the same size. How about using crankshafts instead of a belt driven system? Weight can be reduced with creative use of materials (carbon fiber or fiberglass shafts).

I have some suggestions: for the belt pulleys you can use some with slightly barrel shape that will self center the belt (like on band saw), yet giving the power transmitted, the pulleys should have shoulders to keep the belt flying. Or you can use a transmission box like two mikey mouses heads connected at the neck: two big gears, one connected to the engine, the other used to reverse the rotation, and for each one 2 smaller gears to send the power to the propellers using shafts (either via 2 sets of conic gears if the engine and propellers are level, or if the engine is very low shafts with universal joints).

As far the the barrel shaped pulleys belts go, I'm using those for the flat sided idlers. All the toothed pulleys are flat faced, but they all do have shoulders. You can't have the barrel shape and still maintain the right tooth profile.

I did look into gearboxes as well, but they are too heavy for what I need.

_____ | | | this is a combination of cylindrical and conical gear|__|__| the cylindrical part engages the other identical gear\ | / the conical engages the shaft conical gear ----- for each of these gears there are two shafts for two propellers

The only issue is that you'll have adjacent propellers rotating in the same direction (but you already choosed this configuration). You can also use sliding shafts to counter the bends in the propellers trusses.

Yes. I originally wanted to build a quadcopter large enough to carry a single person. However getting a more powerful engine and the hardware to go with it would have been expensive. I chose to make a smaller (relatively) prototype to test out the technology needed before going bigger.

Awesome work Peter! The wider belts do seem to be working out pretty well. I've made the same mistake leaving the screw out of a servo. I bet you needed a change of shorts after the unexpected jump to full throttle!

Very interesting project! Like many others, I'm curious as to how controlling thrust direction will replace variable prop pitch or speed.

Also, what is the estimated full-up weight at take-off? Current AMA guidelines are that any model weighing in at more than 50 pounds should be registered as an experimental aircraft. Needless to say, this bad boy is going to be potentially lethal, making sure you're within the rules is a good investment.

Thanks for the interest! I'm hoping to have a gross takeoff weight of 240 lbs, with 40 lbs of payload capacity. Your right, Goliath can be hazardous and this is not something you simply take to the park and fly around.

Your right, knowing what the rules are is a good investment. I'm curious if you happen to have a link to the guidelines you're referring to. I did some looking and found AMA document 520A (http://www.modelaircraft.org/files/520-a.pdf). It simply states that AMA Large Model Aircraft 1 (LMA1) can be from 50 to 77.2 lbs and LMA2 can be from 77.3 to 150 lbs.
I did find a reference to the IMAA guidelines that states:
"IMAA qualification also requires the RC model be a maximum weight of 55 pounds, with fuel – ready to fly. Models over this weight up to 100 pounds, with fuel – ready to fly (known as Experimental Radio Controlled Aircraft) may also qualify as IMAA giant scale provided they have a Permit To Fly signed by an AMA certified “Experimental Inspector”"

My understanding is that drones are currently certificated by the FAA, and the guidelines that they are working on will be valid for 55 lbs and below. So this leaves Goliath in a questionable area. I'm not sure where I'll be able to fly it once it is flying. For now I'll just have to worry about it once I get Goliath flying.

Heres the "if" and I dont now if it will work... See if you can find an alternator and a flight controller. There are lots of electric ones, although it may need to be retooled but this will allow you to balance the quad with the brushless motors. The motors would be powered by the gas engine turning the alternator, well besides the initial first charge.

At the most maybe, it would need to be tuned to stay afloat, however instead of the rotors providing primary lift the engine would therefore making it more powerful and using the rotors for stabilization and guidance using the flight controller. That may need to be tuned im sure the physics are different. Although with the *hanging* design of having the motor propeller and camera/gimbal lower it should make stabilization a bit easier.

A thought I had bouncing around. In any case thought i'd throw it your way, never know.

Thanks for the inputs. This is what I feel Hackaday.io is all about, so please keep the inputs coming. The issues I've been having are oscillations with the belts themselves, I hope I have it fixed, but I haven't tested out the latest config.
A hybrid design would be nice, it certainly would solve the issues of having belts. I haven't done the math as to how much power I would need to maneuver using electrical power. The engine is already equipped with an alternator, so it'd just be extra weight of the control motors. Something to think about if the current fixes don't work out. Thanks!

Also for fairly decent cheap parts this place is the place to look. Couldnt believe the prices so i'd question the build quality long term however for a working concept and for ideas on what to look for. This place has got the parts.

Also the idea to lower the engine and main rotor a bit came from here.

Look at the very bottom, theres the degrees of inclination. The lower center of gravity at the center as well makes it more stabile. Also.....

If you were to go with a single gas propellery and smaller control engines on the outside. I would use a propeller with a center connect and outside connection ring. Fix the propeller inside a round shell. That way it would have the stability if you wanted, to even attach the 4 control engines above the main main blade itself. It might offer a bit more stability as well, keeping the propeller blade from oscillating, attached to the motor.

I have added spring loaded adjustable tensioners, that I built from scratch. They can be seen in the video link here.
https://www.youtube.com/watch?v=OfnLvJodg84Hopefully the remaining issue was having the pulley flanges setup right. Hopefully I'll find out it's all right with the next test.

Oooh oh I dont know about springs. Makes it bouncy thats not good. I would have use screw adjustible ones you can lock into place. Especially because depending on temperature and wear the belts will loosen and tighten (dont know about you but its getting cold here XD)

If all else fails. I highly suggest looking at a chain based solution. Grab a couple old bikes for the gears and chains from thrift or garage sales.